1. Field of the Invention
The present invention relates generally to Magnetic Resonance Imaging (MRI), and more particularly to systems and methods for generating an MRI elastograph of a region in a body using an acoustic transducer.
2. Background
A hydrogen atom, which has a single proton in its nucleus, exhibits a nuclear spin that produces a small magnetic moment vector. In the presence of a magnetic field, the magnetic moment vector of the hydrogen atom tends to align in the direction of the magnetic field. In addition, the nuclear spin of the hydrogen atom exhibits a resonance frequency, which is a function of the magnetic field strength and is approximately 42.85 MHz per Tesla.
The magnetic properties of the hydrogen atom are exploited in Magnetic Resonance Imaging (MRI) to generate an image of the interior of a human body. MRI images the interior of the body by measuring the hydrogen atom density at different positions inside the body. Because different tissues in the body have different hydrogen atom densities, MRI is able to translate the hydrogen atom density measurement into an image of the body.
MRI is used in a medical imaging technique called Magnetic Resonance Elastography (MRE) to image the relative stiffness of different regions inside the body. MRE stems from the importance of palpation in the diagnosis of certain cancers and tumors. Physicians typically use palpation to detect a tumor in the body by assessing the difference in stiffness between the tumor and the surrounding healthy tissue.
To image the relative stiffness of different regions inside a human body using MRE, an acoustic wave is applied to the body. The acoustic wave generates shear waves that propagate through the body. MRI is used to image the shear waves as they propagate through the body. The wavelength of the shear waves depends upon the stiffness of the body tissue through which they propagate. The wavelength is shorter in softer, more easily deformed, body tissue and is longer in harder body tissue. Several MRI images of the shear waves are taken at different acquisition times. The MRI wave images are then processed to generate an elastograph, which provides an image of the relative stiffness of different regions inside the body. The elastograph provides high contrast between soft and hard body tissue. This may be especially useful for the detection of tumors, which tend to be stiffer than the surrounding tissue.
Despite the advances in medical technology, further improvements in imaging tissues within the human body are required.